:root {
  /* Facebook-inspired color palette from source-aligned values */
  --bg: #f0f2f5;           /* Light grey background [1] */
  --card: #ffffff;         /* White cards [2] */
  --text: #1c1e21;         /* Near-black primary text [1] */
  --muted: #65676b;         /* Grey muted text [2] */
  --accent: #1877f2;       /* Facebook Blue [2] */
  --line: #dddfe2;         /* Light grey separators [2] */
}

* { box-sizing: border-box; }

body { 
  margin: 0; 
  /* Elegant font stack including Segoe UI and system fonts [1, 6] */
  font-family: system-ui, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; 
  background: var(--bg); 
  color: var(--text); 
  font-size: 16px; /* Standard base size [1] */
}

a { color: var(--accent); text-decoration: none; font-weight: 600; }
a:hover { text-decoration: underline; }

.container { max-width: 1100px; margin: 0 auto; padding: 18px; }

.topbar {
  display: flex; 
  align-items: center; 
  justify-content: space-between;
  padding: 12px 18px; 
  background: var(--card); 
  /* Subtle depth using box-shadow [2, 5] */
  box-shadow: 0 2px 4px rgba(0, 0, 0, .1); 
  border-bottom: 1px solid var(--line);
  position: sticky; /* Keeps the navigation visible [7] */
  top: 0;
  z-index: 100;
}

.brand { 
  font-size: 24px; 
  font-weight: 800; 
  color: var(--accent); 
  letter-spacing: -1px; 
}

.nav a { 
  margin-left: 12px; 
  color: var(--muted); 
  padding: 8px 12px; 
  border-radius: 8px; /* Rounded interactive areas [4] */
}

.nav a:hover { 
  background: rgba(0, 0, 0, .05); 
  text-decoration: none; 
}

.notification-badge {
  background-color: #f02849; /* Alert red */
  color: #ffffff;
  font-size: 10px;
  padding: 2px 6px;
  border-radius: 10px; /* Rounded pill style typical of notifications [4] */
  margin-left: 5px;
  vertical-align: middle;
  border: 1px solid #ffffff;
}

.card {
  background: var(--card);
  border-radius: 8px; /* Standard rounded corners for modern web [4, 8] */
  padding: 16px;
  margin: 16px 0;
  /* Soft shadow for the "card" effect [2, 9] */
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1), 0 2px 4px rgba(0, 0, 0, 0.1);
  border: 1px solid var(--line);
}

h1, h2, h3 { margin: 0 0 12px; color: var(--text); }

label { 
  display: block; 
  margin: 10px 0 6px; 
  font-weight: 600; 
  color: var(--text); 
  font-size: 14px; 
}

input, textarea, select {
  width: 100%;
  padding: 12px;
  background: #f5f6f7;
  border: 1px solid var(--line);
  color: var(--text);
  border-radius: 6px; /* Slightly rounded inputs [10] */
  outline: none;
  font-size: 15px;
}

input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 2px rgba(24, 119, 242, .2); /* Focus ring effect [11] */
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 20px;
  border-radius: 6px; /* Buttons with soft rounded corners [2, 12] */
  border: none;
  font-weight: 600;
  font-size: 15px;
  cursor: pointer;
  transition: background 0.2s; /* Smooth interaction [13] */
}

.btn.primary { 
  background: var(--accent); 
  color: #ffffff; 
}

.btn.primary:hover { 
  background: #166fe5; /* Slightly darker blue on hover [2] */
}

.btn.danger { 
  background: #f02849; 
  color: #ffffff; 
}

.muted { color: var(--muted); font-size: 14px; }

.hr { 
  height: 1px; 
  background: var(--line); 
  margin: 16px 0; 
}

.profile-shell {
  border: 1px solid var(--line);
  padding: 16px;
  border-radius: 8px;
  background: #f9f9f9;
}

.footer {
  text-align: center;
  padding: 24px;
  font-size: 13px;
  color: var(--muted);
}